Immunocytochemical staining with enkephalin (ENK) antiserum revealed immunoreactive stalked cells in lamina II. Dorsal column postsynaptic spinomedullary neurons (DCPS) were retrogradely labeled with HRP in cats and monkeys. The lumbosacral enlargements of both species contained about 1,000 DCPS neurons. It is thus apparent that the DCPS system is one of the major sources of somatosensory input to the brain. Four types of DCPS neurons were characterized on the basis of the shape and orientation of their dendritic arbors. Electrophysiological analysis of antidromically identified DCPS neurons shows that about half respond only to tactile stimuli while the remainder respond also to noxious stimuli. Intracellular recordings show that many DCPS neurons respond to primary afferent input with an epsp-ipsp sequence. The ipsp is probably initiated by A-beta, low threshold mechanoreceptors. its amplitude is frequency dependent in the range of 5-20 Hz. When retrogradely labeled DCPS neurons were immunocytochemically counterstained with a 5-HT antiserum, numerous 5-HT axonal varicosities were seen to contact the DCPS perikarya and proximal dendrites.